Inhibition of aflatoxins on UDP-glucuronosyltransferases (UGTs).

Aflatoxins have been recognized as the most harmful mycotoxins leading to various toxic effects. The present study aims to determine the inhibition behavior of aflatoxins on the activity of the important phase II metabolizing enzymes, UDP-glucuronosyltransferases (UGTs), based on in vitro incubation system of recombinant human UGTs-catalyzed glucuronidation of 4-methylumbelliferone (4-MU). 100 µM AFB1 and AFG1 exhibited extensive inhibition towards UGT isoforms especially UGT1A7 and UGT1A8, with the inhibition ratios to be 71.38%, 72.95% and 72.79% for AFB1 to UGT1A7, AFB1 to UGT1A8 and AFG1 to UGT1A8, respectively. Molecular docking results showed that hydrogen bonds and hydrophobic contacts of the particular structure consisting of double furan ring with double bond contributed to the interaction of aflatoxins and UGTs. Kinetics analysis, including inhibition types and kinetics parameters (Ki), and in vitro-in vivo extrapolation (IVIVE) indicated that there might be a medium possibility of inhibition on UGTs by aflatoxins in vivo. In conclusion, the present study indicated that aflatoxins could possibly disturb endogenous metabolism by inhibiting the activity of UGTs so as to exhibit toxic effects.

Impact of pregnancy related hormones on drug metabolizing enzyme and transport protein concentrations in human hepatocytes.

Pregnancy alters the disposition and exposure to multiple drugs indicated for pregnancy-related complications. Previous in vitro studies have shown that pregnancy-related hormones (PRHs) alter the expression and function of certain cytochrome P450s (CYPs) in human hepatocytes. However, the impact of PRHs on hepatic concentrations of non-CYP drug-metabolizing enzymes (DMEs) and transport proteins remain largely unknown. In this study, sandwich-cultured human hepatocytes (SCHH) from five female donors were exposed to vehicle or PRHs (estrone, estradiol, estriol, progesterone, cortisol, and placental growth hormone), administered individually or in combination, across a range of physiologically relevant PRH concentrations for 72 h. Absolute concentrations of 33 hepatic non-CYP DMEs and transport proteins were quantified in SCHH membrane fractions using a quantitative targeted absolute proteomics (QTAP) isotope dilution nanoLC-MS/MS method. The data revealed that PRHs altered the absolute protein concentration of various DMEs and transporters in a concentration-, isoform-, and hepatocyte donor-dependent manner. Overall, eight of 33 (24%) proteins exhibited a significant PRH-evoked net change in absolute protein concentration relative to vehicle control (ANOVA p < 0.05) across hepatocyte donors: 1/11 UGTs (9%; UGT1A4), 4/6 other DMEs (67%; CES1, CES2, FMO5, POR), and 3/16 transport proteins (19%; OAT2, OCT3, P-GP). An additional 8 (24%) proteins (UGT1A1, UGT2B4, UGT2B10, FMO3, OCT1, MRP2, MRP3, ENT1) exhibited significant PRH alterations in absolute protein concentration within at least two individual hepatocyte donors. In contrast, 17 (52%) proteins exhibited no discernable impact by PRHs either within or across hepatocyte donors. Collectively, these results provide the first comprehensive quantitative proteomic evaluation of PRH effects on non-CYP DMEs and transport proteins in SCHH and offer mechanistic insight into the altered disposition of drug substrates cleared by these pathways during pregnancy.

Pregnancy-Related Hormones Increase UGT1A1-Mediated Labetalol Metabolism in Human Hepatocytes.

Pregnancy-related hormones (PRH) are recognized as important regulators of hepatic cytochrome P450 enzyme expression and function. However, the impact of PRH on the hepatic expression and function of uridine diphosphate glucuronosyltransferases (UGTs) remains unclear. Using primary human hepatocytes, we evaluated the effect of PRH exposure on mRNA levels and protein concentrations of UGT1A1, UGT2B7, and other key UGT enzymes, and on the metabolism of labetalol (a UGT1A1 and UGT2B7 substrate commonly prescribed to treat hypertensive disorders of pregnancy). Sandwich-cultured human hepatocytes (SCHH) from female donors were exposed to the PRH estradiol, estriol, estetrol, progesterone, and cortisol individually or in combination. We quantified protein concentrations of UGT1A1, UGT2B7, and four additional UGT1A isoforms in SCHH membrane fractions and evaluated the metabolism of labetalol to its glucuronide metabolites in SCHH. PRH exposure increased mRNA levels and protein concentrations of UGT1A1 and UGT1A4 in SCHH. PRH exposure also significantly increased labetalol metabolism to its UGT1A1-derived glucuronide metabolite in a concentration-dependent manner, which positively correlated with PRH-induced changes in UGT1A1 protein concentrations. In contrast, PRH did not alter UGT2B7 mRNA levels or protein concentrations in SCHH, and formation of the UGT2B7-derived labetalol glucuronide metabolite was decreased following PRH exposure. Our findings demonstrate that PRH alter expression and function of UGT proteins in an isoform-specific manner and increase UGT1A1-mediated labetalol metabolism in human hepatocytes by inducing UGT1A1 protein concentrations. These results provide mechanistic insight into the increases in labetalol clearance observed in pregnant individuals.

Effect of molecular weight of polyethylene glycol on pharmacokinetics of baicalin / 药学学报

The aim of this study was to investigate the effects of polyethylene glycol (PEGs) with different molecular weights (MW: 400, 1 000, 4 000) on the pharmacokinetics of baicalin, and preliminarily analyze its mechanism. Rats were gavaged with baicalin (168 mg·kg-1) + aqueous solution or baicalin + PEGs solution and plasma samples were collected from 0 to 24 h after administration. The concentration of baicalin and its main metabolite baicalein 6-O-β-D-glucuronide (B6G) were determined at different time points by UPLC-MS/MS, and the pharmacokinetic parameters were calculated with DAS 3.0 software. The results showed that PEGs with different molecular weights could effectively increase the AUC0-t of baicalin and B6G, increase the Cmax, and prolong the t1/2, effectively increasing the concentration of baicalin and B6G in vivo. The mechanism may be by promoting the activity of uridine diphosphate glucuronosyl-transferases 1A8 (UGT1A8) and 1A9 (UGT1A9), thereby increasing the transformation rate of baicalin and B6G. The rate of metabolism of B6G was faster than that of baicalin, suggesting that PEGs had a higher affinity for UGT1A8, and PEG400 had the most significant effect. The purpose of this study was to provide a basis for the clinical safe use of baicalin and other flavonoids and the design of new dosage forms with the participation of PEGs. The animal experiment protocol in this study was approved by the Experimental Animal Ethics Committee of Guizhou Medical University.

Advances in biosynthesis of triterpenoid saponins in medicinal plants.

In recent years, biosynthesis of triterpenoid saponins in medicinal plants has been widely studied because of their active ingredients with diverse pharmacological activities. Various oxidosqualene cyclases, cytochrome P450 monooxygenases, uridine diphosphate glucuronosyltransferases, and transcription factors related to triterpenoid saponins biosynthesis have been explored and identified. In the biosynthesis of triterpenoid saponins, the progress of gene mining by omics-based sequencing, gene screening, gene function verification, catalyzing mechanism of key enzymes and gene regulation are summarized and discussed. By the progress of the biosynthesis pathway of triterpenoid saponins, the large-scale production of some triterpenoid saponins and aglycones has been achieved through plant tissue culture, transgenic plants and engineered yeast cells. However, the complex biosynthetic pathway and structural diversity limit the biosynthesis of triterpenoid saponins in different system. Special focus can further be placed on the systematic botany information of medicinal plants obtained from omics large dataset, and triterpenoid saponins produced by synthetic biology strategies, gene mutations and gene editing technology.

Elevated system exposures of baicalin after combinatory oral administration of rhein and baicalin: Mainly related to breast cancer resistance protein (ABCG2), not UDP-glucuronosyltransferases.

ETHNOPHARMACOLOGICAL RELEVANCE: A traditional Chinese medicine (TCM) prescription follows the principle of compatibility (peiwu) to achieve the fundamental purpose: to increase efficacy and reduce toxicity. Rhei rhizoma, commonly known as Chinese rhubarb, is the most frequently used herb with Radix Scutellariaee. This classic fixed compatibility is considered for heat-clearing, qi regulation and detoxifying to gain better efficacy and reduce cytotoxicity with respect to unilateral medicine. With this in mind, we propose it is highly promising to find ingredients in rhubarb to increase the bioavailability of baicalin. AIM OF STUDY: In the present study, effect of rhien on pharmacokinetic profile of baicalin in rat plasma was investigated, and the underlying mechanisms were partly dissected through intestinal absorption, metabolism and biliary excretion with in vivo, in vitro and in situ assays. MATERIALS AND METHODS: Pharmacokinetic analysis in rats was first performed to provide a general overview of the in vivo exposure of baicalin and rhein after co-administration, while the biliary excretion study provided insight to the effect of rhein on the transport of baicalin from hepatocytes to bile. In vitro incubation and inhibition studies in human/rat liver microsome and human/rat intestinal S9 fraction were conducted to elucidate the role of uridine diphosphate-glucuronosyltransferases (UGTs) on the hepatic and intestinal metabolism of baicalein (the aglycone of baicalin), and to determine whether rhein can affect the UGT-mediated glucuronidation of baicalein. In situ intestinal perfusion study was designed to investigate the effect of rhein on intestinal absorption of baicalin, and breast cancer resistance protein (BCRP) inhibitor was co-perfused as positive control to demonstrate the role of the efflux transporter, while BCRP-MDCK II cell(Madin-Daby canine kidney cell) model was used as an in vitro approach to further confirm the conclusion. RESULTS: The AUC and Cmax of baicalin were increased to 189.93% and 305.73%, respectively, and the clearance of baicalin was significantly decreased from 4.17 ± 2.40 to 1.65 ± 0.79 L/h/kg following oral co-administration of rhein. The AUC of baicalin was markedly increased and the biliary clearance was significantly decreased when baicalin and rhein were co-administered intravenously. The effect of rhein on the glucuronidation of baicalein in various subcellular fractions was examined, and it was found that rhein did not affect the UGT-mediated glucuronidation of baicalein. Results of in situ intestinal perfusion revealed that co-perfusion with Ko143 (a potent BCRP inhibitor) or rhein significantly reduced the cumulative excretion amount of baicalin, from 9.27 ± 2.79 to 2.80 ± 0.97 or 4.84 ± 0.60 nM, respectively. Additionally, the efflux ratio Papp(BL-AP)/Papp(AP-BL) of baicalin in BCRP-MDCK II was decreased significantly in the presence of rhein or Ko143, which meant rhein could inhibit the BCRP-mediated efflux transport of baicalin. CONCLUSIONS: These results indicated that rhein can increase the bioavailability of baicalin by inhibiting BCRP-mediated efflux transport of baicalin in enterocytes and hepatocytes rather than by affecting the activity of UGT enzyme.

Advances in biosynthesis of triterpenoid saponins in medicinal plants / 中国天然药物

In recent years, biosynthesis of triterpenoid saponins in medicinal plants has been widely studied because of their active ingredients with diverse pharmacological activities. Various oxidosqualene cyclases, cytochrome P450 monooxygenases, uridine diphosphate glucuronosyltransferases, and transcription factors related to triterpenoid saponins biosynthesis have been explored and identified. In the biosynthesis of triterpenoid saponins, the progress of gene mining by omics-based sequencing, gene screening, gene function verification, catalyzing mechanism of key enzymes and gene regulation are summarized and discussed. By the progress of the biosynthesis pathway of triterpenoid saponins, the large-scale production of some triterpenoid saponins and aglycones has been achieved through plant tissue culture, transgenic plants and engineered yeast cells. However, the complex biosynthetic pathway and structural diversity limit the biosynthesis of triterpenoid saponins in different system. Special focus can further be placed on the systematic botany information of medicinal plants obtained from omics large dataset, and triterpenoid saponins produced by synthetic biology strategies, gene mutations and gene editing technology.

Interactions of drug-metabolizing enzymes with the Chinese herb Psoraleae Fructus.

Psoraleae Fructus (the dried fruits of Psoralea corylifolia), one of the most frequently used Chinese herbs in Asian countries, has a variety of biological activities. In clinical settings, Psoraleae Fructus or Psoraleae Fructus-related herbal medicines frequently have been used in combination with a number of therapeutic drugs for the treatment of various human diseases, such as leukoderma, rheumatism and dysentery. The use of Psoraleae Fructus in combination with drugs has aroused concern of the potential risks of herb-drug interactions (HDI) or herb-endobiotic interactions (HEI). This article reviews the interactions between human drug-metabolizing enzymes and the constituents of Psoraleae Fructus; the major constituents in Psoraleae Fructus, along with their chemical structures and metabolic pathways are summarized, and the inhibitory and inductive effects of the constituents in Psoraleae Fructus on human drug-metabolizing enzymes (DMEs), including target enzyme(s), its modulatory potency, and mechanisms of action are presented. Collectively, this review summarizes current knowledge of the interactions between the Chinese herb Psoraleae Fructus and therapeutic drugs in an effort to facilitate its rational use in clinical settings, and especially to avoid the potential risks of HDI or HEI through human DMEs.

Charactering the metabolism of cryptotanshinone by human P450 enzymes and uridine diphosphate glucuronosyltransferases in vitro.

Cryptotanshinone (CT) is the main active component in the root of Salvia miltiorrhiza Bunge (SMB) that displays antibacterial, anti-inflammatory and anticancer activities. In this study, we characterized phase I and phase II metabolism of CT in human liver microsomes in vitro and identified the metabolic enzymes (CYPs and UGTs) involved. The metabolites of CT generated by CYPs were detected using LC-MS/MS and the CYP subtypes involved in the metabolic reactions were identified using chemical inhibitors of CYP enzymes and recombinant human CYP enzymes (CYP1A2, CYP2A6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, and CYP3A4). Glucuronidation of CT was also examined, and the UGT subtypes involved in the metabolic reactions were identified using recombinant human UGT enzymes (1A1, 1A3, 1A4, 1A5, 1A6, 1A7, 1A8, 1A9, 1A10, 2B4, 2B7, 2B15 and 2B17). After adding NADPH to the human liver microsomes incubation system, CT was transformed into 6 main dehydrogenation and hydroxylation metabolites. CYP2A6, CYP3A4 and CYP2C19 were the major contributors to the transformation of its hydroxylation metabolites. CYP2C19, CYP1A2 and CYP3A4 were the major contributors to the transformation of its hydrogenation metabolites in human liver microsomes. This study showed that the metabolites at m/z of 473 were mediated by UGT1A9 and that the metabolites at m/z of 489 were mediated by UGT2B7 and UGT2B4. CT was extensively metabolized by UGTs following metabolism by CYPs in the liver.

Inhibitory effects of fifteen phthalate esters in human cDNA-expressed UDP-glucuronosyltransferase supersomes.

Phthalate esters (PAEs) have been extensively used in industry as plasticizers and there remains concerns about their safety. The present study aimed to determine the inhibition of phthalate esters (PAEs) on the activity of the phase II drug-metabolizing enzymes UDP-glucuronosyltransferases (UGTs). In vitro recombinant UGTs-catalyzed glucuronidation of 4-methylumbelliferone was used to investigate the inhibition potentials of PAEs towards various s UGTs. PAEs exhibited no significant inhibition of UGT1A1, UGT1A3, UGT1A8, UGT1A10, UGT2B15, and UGT2B17, and limited inhibition of UGT1A6, UGT1A7 and UGT2B4. However, UGT1A9 was strongly inhibited by PAEs. In silico docking demonstrated a significant contribution of hydrogen bonds and hydrophobic interactions contributing to the inhibition of UGT by PAEs. The Ki values were 15.5, 52.3, 23.6, 12.2, 5.61, 2.79, 1.07, 22.8, 0.84, 73.7, 4.51, 1.74, 0.58, 6.79, 4.93, 6.73, and 7.23 µM for BBOP-UGT1A6, BBZP-UGT1A6, BBOP-UGT1A7, BBZP-UGT1A7, DiPP-UGT1A9, DiBP-UGT1A9, DCHP-UGT1A9, DBP-UGT1A9, BBZP-UGT1A9, BBOP-UGT1A9, DMEP-UGT1A9, DPP-UGT1A9, DHP-UGT1A9, DiBP-UGT2B4, DBP-UGT2B4, DAP-UGT2B4, and BBZP-UGT2B4, respectively. In conclusion, exposure to PAEs might influence the metabolic elimination of endogenous compounds and xenobiotics through inhibiting UGTs.

Relationship between single nucleotide polymorphisms of UGT1A6 and aspirin low responsiveness in patients with ischemic stroke / 中华神经科杂志

Objective To investigate the relationship between single nucleotide polymorphisms (SNPs) of UGT1 A6 and aspirin response in a cohort of Chinese Han population.Methods A total of 323 ischemic stroke patients consecutively registered in Nanjing Stroke Registry Program from September 2011 to October 2014 were enrolled.Three SNPs (rs6759892,rs2070959 and rs1105879) of UGT1A6 were genotyped in these ischemic stroke patients.Association of genotypes and aspirin response was evaluated by generalized linear model.Indicated with the inhibition rate of platelets,aspirin response was assessed by thromboelastograph.Results The mutation allele (G) of rs2070959 was positively related to platelets inhibition (β =0.084,P =0.010,Pcorrected =0.029),especially in male (β =0.098,P =0.006,Pcorrected =O.019).The dominant models of rs6759892,rs1105879 were also modestly related to aspirin response (P=0.015,Pcorrected=0.046 in both SNPs) in male.Thus the polymorphisms of UGT1A6 showed a relationship with aspirin response,especially in males.Conclusions The results indicated that genetic polymorphism of UGT1A6 might have an effect on individuals' aspirin response,especially in males.These findings can help clinicians to optimize the antiplatelet therapy for ischemic stroke patients.

In vitro metabolism of canagliflozin in human liver, kidney, intestine microsomes, and recombinant uridine diphosphate glucuronosyltransferases (UGT) and the effect of genetic variability of UGT enzymes on the pharmacokinetics of canagliflozin in humans.

O-glucuronidation is the major metabolic elimination pathway for canagliflozin. The objective was to identify enzymes and tissues involved in the formation of 2 major glucuronidated metabolites (M7 and M5) of canagliflozin and subsequently to assess the impact of genetic variations in these uridine diphosphate glucuronosyltransferases (UGTs) on in vivo pharmacokinetics in humans. In vitro incubations with recombinant UGTs revealed involvement of UGT1A9 and UGT2B4 in the formation of M7 and M5, respectively. Although M7 and M5 were formed in liver microsomes, only M7 was formed in kidney microsomes. Participants from 7 phase 1 studies were pooled for pharmacogenomic analyses. A total of 134 participants (mean age, 41 years; men, 63%; white, 84%) were included in the analysis. In UGT1A9*3 carriers, exposure of plasma canagliflozin (Cmax,ss , 11%; AUCτ,ss , 45%) increased relative to the wild type. An increase in exposure of plasma canagliflozin (Cmax,ss , 21%; AUCt,ss , 18%) was observed in participants with UGT2B4*2 genotype compared with UGT2B4*2 noncarriers. Metabolites further delineate the role of both enzymes. The pharmacokinetic findings in participants carrying the UGT1A9*3 and UGT2B4*2 allele implicate that UGT1A9 and UGT2B4 are involved in the metabolism of canagliflozin to M7 and M5, respectively.

Genetic Polymorphisms of UGT1A and their Association with Clinical Factors in Healthy Koreans

Glucuronidation by the uridine diphosphateglucuronosyltransferase 1A enzymes (UGT1As) is a major pathway for elimination of particular drugs and endogenous substances, such as bilirubin. We examined the relation of eight single nucleotide polymorphisms (SNPs) and haplotypes of the UGT1A gene with their clinical factors. For association analysis, we genotyped the variants by direct sequencing analysis and polymerase chain reaction (PCR) in 218 healthy Koreans. The frequency of UGT1A1 polymorphisms, -3279T>G, -3156G>A, -53 (TA)(6>7), 211G>A, and 686C>A, was 0.26, 0.12, 0.08, 0.15, and 0.01, respectively. The frequency of -118 (T)9>10 of UGT1A9 was 0.62, which was significantly higher than that in Caucasians (0.39). Neither the -2152C>T nor the -275T>A polymorphism was observed in Koreans or other Asians in comparison with Caucasians. The -3156G>A and -53 (TA)6>7 polymorphisms of UGT1A were significantly associated with platelet count and total bilirubin level (p=0.01, p=0.01, respectively). Additionally, total bilirubin level was positively correlated with occurrence of the UGT1A9-118 (T)(9>10) rare variant. Common haplotypes encompassing six UGT1A polymorphisms were significantly associated with total bilirubin level (p=0.01). Taken together, we suggest that determination of the UGT1A1 and UGT1A9 genotypes is clinically useful for predicting the efficacy and serious toxicities of particular drugs requiring glucuronidation.